Ear pain (otalgia) is one of the most common reasons for visits to primary care physicians and medical care providers [1,2]. Causes include inner ear infections (otitis media), external ear infections (otitis externa), foreign bodies and trauma [1]. Otitis media is the most common cause of ear pain, occurs primarily in young children, peaks during the winter months and is associated with respiratory infections [3]. In contrast, otitis externa is regularly associated with swimming and diving (often called “swimmer’s ear”), [4-6], affects all ages [7-9] and peaks during the summer [7,10]. However, because outer ear infections can develop anywhere from hours to days after exposure, they may not always be accurately attributed to swimming or other water exposures [11]. Moisture, humidity and water in the ear canal are thought to remove the protective lining (cerumen, or ear wax) and increase the pH, increasing susceptibility to infection [8]. Among divers, otitis externa was associated with a change in the normal microbial flora from Gram-positive to Gram-negative species shortly after immersion [12]. Pseudomonas aeruginosa, Staphylococcus epidermidis and Staphylococcus aureus are the bacterial agents most frequently isolated from the ear canal of those diagnosed with otitis externa [10]. Some studies have linked the presence of Pseudomonas aeruginosa in waterbodies to cases of otitis externa in swimmers [13,14].

The health-care burden associated with earaches and ear infections is considerable. An estimated 2.4 million U.S. health-care visits (8.1 visits per 1,000 population) were associated with a diagnosis of acute otitis externa (ambulatory care or emergency room) in 2007 [15]. To develop estimates of the incidence and health burden of earache directly attributable to swimming in natural waters, we used data from over 50,000 beachgoers enrolled in the National Environmental and Epidemiological Assessment of Recreational Water Study (NEEAR Water Study) at nine beach sites (4 marine, 5 freshwater) [16-18].

Data collected from a survey of over 50,000 beachgoers were used to estimate the incidence and burden of earaches resulting from swimming in natural waters. For every 1000 swimming events in natural waters there were slightly more than 7 excess earaches. The effect we observed was relatively constant across beach sites and age groups. Although young children reported a higher overall incidence of earache, the risk associated with swimming exposure was slightly lower than other age groups. This is consistent with the age distribution of otitis externa which affects all age groups [7,8], and young children are not necessarily at higher risk. Earaches in young children and infants are often attributable to otitis media and very young children are also unlikely to experience extensive head-immersion swimming exposures.

The health care burden and economic impacts of swimming-associated earaches are substantial. The National Survey on Recreation and the Environment [23] estimated 41.3% (weighted to represent the United States population) of the population over 16 years of age had “Swam in a Lake, Ocean or Stream” during the past year. Assuming this percentage applies to the 2011 total United States population of 311,591,917 [24], the number of people who swim at least once per year in a natural waterbody is estimated as: 41.3% × 311,591,917 = 128,687,462. Applying the excess risk ER(E) estimate of 7.12 per 1,000 swimming events in natural waters results in 916,000 earaches due to these swimming exposures. Assuming the burden estimates we observed apply nationally, these earaches would result in 260,000 visits to the doctor, 39,900 visits to the emergency room and nearly $4 million dollars spent on prescription and over-the-counter medications due to earaches associated with swimming in natural waters. Since most people who swim likely do so numerous times each year (the NRSE only reported those who reported any swimming in lakes, oceans or streams annually), these are likely underestimates.

The costs for over-the-counter and prescription medications reported by participants are a fraction of the direct health care cost of earache. The average cost of a doctor’s office or emergency room visit for otitis externa (including out-of-pocket and insurer costs for the visit and prescription medication) has been estimated to be $200 [15]. Assuming these costs apply to earache, this implies $59,980,000 in direct health care costs to patients and insurers (260,000 office visits + 39,900 emergency room visits × $ 200). Additionally, each visit was estimated to occupy 15 minutes of clinician time, resulting in 74,975 hours of clinician time (299,900 visits × 0.25 hours/visit) spent on visits for earache attributable to swimming in natural waters. Roughly one-third of those visits could be expected to result in prescriptions for systemic antimicrobial medications, instead of recommended topical antimicrobials [25], equivalent to 98,967 antimicrobial prescriptions ( 299,900×13) attributable to swimming in natural waters. Such systemic antibiotic prescriptions may often be unnecessary in the absence of complicating conditions [25].

In order to estimate the health burden attributable to swimming-associated earache, we assumed that the health burden and impact of earache for all respondents were representative of the swimming-associated fraction. Although we are unaware of evidence to contradict this assumption, we could not directly evaluate it or confirm it with our data.

This analysis also does not consider swimming in pools, water parks and other chlorinated or treated venues. Although swimmer’s ear is known to be associated with these exposures [14], it is unclear whether the excess risk estimates of 7.12 earaches per 1000 swimming events for natural waters would be accurate for these conditions.

Our results are based on self-report of earache. Due to this limitation, we cannot exclude the possibility that at least some of the risk attributable to swimming exposure was a result of over-reporting of earache among swimmers. Swimmers and non-swimmers were unblinded with regard to the primary exposure of interest, head-immersion swimming, and as a result, it is possible that swimmers over-reported earaches based on this knowledge of exposure, resulting in an overestimate of the true excess risk of earache associated with swimming. However this bias, if present, may not have been strong. Subjects reported on numerous symptoms as part of the NEEAR Water study and earaches were not particularly emphasized in relation to these other symptoms. Swimming and non-swimming respondents were therefore probably unlikely to be abnormally or specifically focused on their earache symptoms. Unlike several other symptoms studied, earache was consistently elevated among swimmers relative to non-swimmers across beach sites and age groups. This consistency of effect was not observed for other non-enteric symptoms, and several showed little association with swimming following adjustment for covariates (respiratory, eye irritations) [17,18]. It seems unlikely that a reporting bias, if present, would specifically affect earache and not also affect other types of symptoms. The relatively constant association across age groups is consistent with otitis exerna in that age groups are affected approximately equally. Finally, “earache” is a relatively objective symptom with which most people are familiar with, and self-reported earache has been shown to agree well with medical records [26].

We did not clinically confirm or diagnose any of the self-reported earaches as otitis externa. It is likely that some of the excess earaches were due to trauma or other irritation so we cannot determine the excess risk specifically attributable to otitis externa. Nonetheless, preventative measures can be taken to reduce the risk of ear infections following swimming exposure. Clinical reports recommend the use of earplugs as a preventative measure was well as the use of over-the counter acidifying agents with alcohol or other astringent and drying the ears after swimming with a hair dryer on the lowest setting [4,8].

Earaches were associated with swimming, but not water quality as measured by the fecal indicator bacteria Enterococcus or turbidity. Swimmer density was also not an important determinant of earaches in our data (results not shown). It is possible that earaches were associated with a water quality parameter we did not measure, although consistent associations between otitis externa and water quality have not been established. Some previous studies have linked otitis externa among swimmers to the presence of Pseudomonas aeruginosa in ambient waters [13] and in pools [14], whereas others have not [27,28]. Swimming exposures may also result in conditions (e.g., moisture, humidity, inflammation, or trauma) where normal, endogenous flora of the ear canal can cause otitis externa [8,29]. Moisture from swimming or bathing is a known risk factor for otitis externa and can remove the protective layer of ear wax (cerumen), raise the pH and create conditions favorable to bacterial growth [8]. These changes may also cause itching in the external auditory canal, adding the potential for scratching and subsequent infection. Individual factors which we did not measure also increase susceptibility to otitis externa following swimming such as narrow or partially obstructed ear canals [11]. Duration of time in water, which has been noted as a risk factor for otitis externa in some studies [27] was unassociated with earache among swimmers in our study. Individual susceptibility or other measures of exposure intensity may outweigh the importance of duration in the water in the development of swimming-associated earache.

In summary, from an analysis of over 39,000 beachgoers at nine freshwater and marine beach sites there were 7.12 excess earaches for every 1,000 head immersion swimming events. We further estimated that for every 1,000 swimming events there were 1.73 earaches that resulted in missed work or activity; 1 that resulted in a phone call to a doctor; 2 in visits to a doctor and 0.31 in visits to an emergency room. As there are over 128 million swimming events in natural waters annually, the population health burden attributable to swimming-associated earaches is considerable. Improved estimates of swimming in natural waters will provide a more accurate estimate of the health burden of swimming associated earaches and other health effects related to swimming exposures.

AOR: Adjusted odds ratio; ER: Excess risk; ER(E): Excess earaches associated with head immersion swimming; ER(E, I): Excess swimming-associated earaches resulting in a health impact; AIC: Akaike’s Information Criterion; qPCR: Quantitative polymerase chain reaction; CI: Confidence interval; p: p-value; EPA: United States Environmental Protection Agency; CDC: Centers for Disease Control and Prevention.

The authors declare that they have no competing interests.

TW led data analysis, interpretation, and manuscript preparation. ES led data collection. MB developed the study design. SC provided calculations for health burden estimates. AD oversaw all aspects of the study. All authors read and approved the final manuscript.